Avoid overlap of points on a timeline (1-D repeling) - r

Question

I want to create a timeline plot that roughly resembles the example below: lots of overlap at some points, not a lot of overlap at others.
What I need: overlapping images should repel each other where necessary, eliminating or reducing overlap. Ideally I'd be able to implement either a vertical or horizontal repel.
library(tidyverse)
library(ggimage)
test_img <- list.files(system.file("extdata", package="ggimage"), pattern="png", full.names=TRUE)
set.seed(123)
df <-
tibble(date = as.Date(paste0("2020-", round(runif(45, 1, 2)), "-", round(runif(45, 1, 10)))),
group = paste0("Timeline ", rep(1:9, each = 5)),
img = sample(test_img, size = 45, replace = T) )
df %>%
ggplot() +
geom_line(aes(x = date, y = group, group = group), size = 5, alpha = 0.2) +
geom_image(aes(x = date, y = group, image = img, group = group), asp = 1)
Something similar to the repelling in ggbeeswarm::geom_beeswarm or ggrepel::geom_text_repel would be nice, but those don't support images. So I think I need to pre-apply some kind of 1-dimensional packing algorithm, implementing iterative pair-wise repulsion on my vector of dates within each group, to try to find a non-overlapping arrangement.
Any ideas? Thank you so much!
Created on 2021-10-30 by the reprex package (v2.0.1)

Answer 1

Here is the solution I’ve been able to come up with, repurposing the circleRepelLayout function from the awesome packcircles package
into the repel_vector vector function that takes in your overlapping vector and a "repel_radius", and returns, if possible, a non-overlapping version.
I demonstrate the solution with the richtext geom since this is a geom I’ve always wished had repel functionality.
library(packcircles)
library(tidyverse)
library(ggtext)
library(ggimage)
repel_vector <- function(vector, repel_radius = 1, repel_bounds = range(vector)){
stopifnot(is.numeric(vector))
repelled_vector <-
packcircles::circleRepelLayout(x = data.frame(vector, ypos = 1, repel_radius),
xysizecols = c("vector", "ypos", "repel_radius"),
xlim = repel_bounds, ylim = c(0,1),
wrap = FALSE) %>%
as.data.frame() %>%
.$layout.x
return(repelled_vector)
}
overlapping_vec <- c(1, 1.1, 1.2, 10, 10.1, 10.2)
repelled_vec_default <- repel_vector(overlapping_vec)
repelled_vec_tighter <- repel_vector(overlapping_vec, repel_radius = 0.35)
ggplot() +
annotate("richtext", x = overlapping_vec, y = 3, label = "**test**", alpha = 0.5) +
annotate("richtext", x = repelled_vec_default, y = 2, label = "**test**", alpha = 0.5) +
annotate("richtext", x = repelled_vec_tighter, y = 1, label = "**test**", alpha = 0.5) +
scale_y_continuous(breaks = 1:3, labels = c("Tighter repel", "Default repel", "Overlapping points"))
In theory you apply this to 2D repelling as well.
To solve the problem in my question, this can be applied like so:
test_img <- list.files(system.file("extdata", package="ggimage"), pattern="png", full.names=TRUE)
set.seed(123)
df <-
tibble(date = as.Date(paste0("2020-", round(runif(45, 1, 2)), "-", round(runif(45, 1, 10)))),
group = paste0("Timeline ", rep(1:9, each = 5)),
img = sample(test_img, size = 45, replace = T) ) %>%
group_by(group) %>%
mutate(repelled_date = repel_vector(as.numeric(date),
repel_radius = 4,
repel_bounds = range(as.numeric(date)) + c(-3,3)),
repelled_date = as.Date(repelled_date, origin = "1970-01-01"))
df %>%
ggplot() +
geom_line(aes(x = date, y = group, group = group), size = 5, alpha = 0.2) +
geom_image(aes(x = repelled_date, y = group, image = img, group = group), asp = 1)
Created on 2021-10-30 by the reprex package (v2.0.1)